Dumbbell



FIG. 1 is a perspective view of a dumbbell showing my new design.

FIG. 2 is a top plan view thereof;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a front view thereof; and,

FIG. 7 is a rear view thereof. 

I claim the ornamental design for a dumbbell, as shown and described. 